The first sermon of Buddha is called Dhammachakkapabattana-sutta. The options given are other sermons or sutras taught by Buddha, but they are not the first sermon.

1. Brahmajalasutta is a discourse given by Buddha on the nature of different views and beliefs. It discusses the 62 wrong views that hinder enlightenment.

3. Kachchayanagottasutta is a discourse in which Buddha explains the characteristics of an ideal monk and the qualities they should possess.

4. Mahaparinirvansutta is a discourse that describes the final days of Buddha`s life and his attainment of parinirvana (final liberation) after his death.

Therefore, the correct answer is option 2 - Dhammachakkapabattana-sutta. It is the first sermon in which Buddha taught the Four Noble Truths, explaining suffering, its cause, its cessation, and the path to liberation.